Turbocharging an internal combustion engine can reduce external emissions and increase the specific power output of the engine, as exhaust departing from the engine cylinders may be directed through a turbine and the resulting energy used to power a compressor. One example configuration integrates the exhaust ports leading from the engine cylinders as well as the turbine housing into the cylinder head itself.
The inventors herein have recognized that achieving exhaust pulse separation enables an exhaust cam duration beneficial to improving fuel consumption, improving low engine speed torque, and achieving better specific power output that current designs. A turbine integrated into the cylinder head will simultaneously reduce cost and decrease the engine footprint. For example, an integrated turbine may decrease the overall size of the system while increasing the efficiency of the engine and the specific power. An integrated axial turbine may also have a faster transient response than a corresponding radial turbine. However, to maintain efficient combustion with long exhaust cam events, residual exhaust gas must be prevented from entering the engine cylinders during an exhaust blowdown event when multiple exhaust valves are open. This is accomplished with full pulse separation of the exhaust gas up to the point where the exhaust gas enters the turbine. In an I-4 engine with a conventional firing order, for example, this may be accomplished by joining the exhaust ports exiting cylinders 1 and 4 together into a first exhaust duct and joining the exhaust ports exiting cylinders 2 and 3 together into a second exhaust duct. The outlets of the two ducts may be connected to the inlet of the turbine.
However, the inventors have also recognized that the current manifold designs that achieve full pulse separation are targeted to radial turbines and may not be applicable to systems that use axial turbines. Incorporating such manifolds may require an external turbocharger, which would increase cost and have a worse transient response.
The above issues may be at least partially addressed, in one example, by a system comprising a cylinder head having a first and second exhaust duct separately coupled to first and second groups of cylinders, each of the first and second exhaust ducts leading to an exhaust driven turbine mounted inside the cylinder head on a bearing, the bearing located within a bearing housing supported by the cylinder head.
In this way, the system may allow pulse separation of exhaust gas exiting the cylinders all the way to an inlet of a turbine, while maintaining a compact configuration. Separating exhaust gas pulses in this way may result in an increase in the efficiency of exhaust gas delivery to a turbine.
Further, the outlets of each of the first and second ducts may form a semi-circular cross-sectional coupling with a gas collector of the turbine, and the two semi-circular cross-sections of each of the first and second outlets may be positioned relative to one another to form an annular combined outlet. In this way, the stator and rotor stages of an axial turbine may be inserted into the opening created in the cylinder head.
In another example, a turbocharged engine comprising a cylinder head forming two or more exhaust ducts, each with an outlet terminus at a turbine wheel or collector, an opening of the outlet terminus of a first exhaust duct being a semi-circular annular shape and an opening of the outlet terminus of a second exhaust output line being a semi-circular annular shape, the outlet termini positioned opposite one another to form a circular annulus. Further, the first exhaust duct may be coupled to outer engine cylinders, and the second exhaust duct may be coupled to inner engine cylinders. In this way, pulse separation may be achieved up to a turbine inserted into the cylinder head within the circular annulus.
In another example, a method, comprising combining, in a cylinder head, exhaust gas from inner inline cylinders of an engine to a first semi-circular annular exit, combining, in the cylinder head, exhaust gas from outer inline cylinders of an engine to a second semi-circular annular exit positioned opposite the first semi-circular annular exit, and directing exhaust gas out of the first and second exits through an axial turbine with bearings mounted in the cylinder head. This method may further comprise adjusting a wastegate valve to adjust flow through a wastegate line positioned in the cylinder head. In this way, the flow of exhaust gas may be controlled within the cylinder head to achieve optimal engine performance.
In other embodiments, the exhaust ducts may enter a turbine collector at a variety of angles to the turbine to achieve the desired relative gas velocity. The outlet terminus of the exhaust ducts may be arranged to cover any variety of sectors of the turbine ranging from half of the turbine circumference to a very small portion of the turbine circumference. This sector configuration may include a unique sector for each cylinder or for groups of cylinders. In this way, pulse separation may be achieved all the way to the turbine collector without combining exhaust pulses.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any of the disadvantages noted above or in any part of this disclosure.